Detector track circuit

ABSTRACT

An alternating current source, normally supplying a basic frequency, is connected to the track section rails through a coupling transformer. In series with the source and transformer primary is a fixed resistance while a fixed inductance is connected in series with the transformer secondary and the rail loop which includes a crossbond between the rails at the distant end. The fixed inductance and resistance are so selected that, when basic frequency energy is supplied with the section unoccupied, equal voltage drops occur across the resistor and the transformer primary which reflects the impedance of the rails, secondary winding, and fixed inductor. Measured signals representing these voltage drops are applied to a voltage comparator. When a train shunt changes the impedance reflected into the transformer primary, the comparator varies the source frequency in order to again equalize the measured voltage drops. Another output from the source is applied to an active type band pass filter which is tuned to the basic frequency and normally energizes a track relay to register an unoccupied track section. However, a shifted frequency output is blocked by the band pass filter and the track relay releases to indicate an occupied track section.

United States Patent i191 Bieder et al.

r [541' DETECTOR TRACK CIRCUIT 3,790,776 2/1974 Rawlins.l....,...; 246/40 Primary Examiner -M. HensonWood, Jr.

Assistant Examiner-George H. Libman i Attorney; Agent, or Firm R. vW.-Mclntire, Jr.; A; G. i Williamson, .Ir.

'An alternating current source, 'normally supplying a basic frequency, is connected to the track section rails through a coupling transformer. In series with the [451 Dec. 17, 1974 ABSTRACT" source and transformer primary is a fixed resistance while a fixed inductance is connected in. series with *the transformer secondary and the rail loop which includes a crossbond between therails at the distant end. The fixed inductance and resistance are so selected that, when basic frequencyenergy is supplied with the section unoccupied, equal voltage drops occur across the resistor and the transformer primary which reflects the impedance of the rails, secondary winding,'and fixed inductor. Measured signals representing these voltage drops are applied to a voltage comparator.'-When a train shunt changes the impedance reflected into the transformer primary,-the comparator varies :the'source frequency in order to again equalize the measured voltage drops. Another output from the source is applied to an active type band pass filter which is tuned to the basic frequency and normally energizes'a track relay to register an unoccupied track section. However, a shifted frequency output is blocked by the band pass filter and the track relay releases to indicate an occupied track section.

10 Claims, 1 Drawing Figure I COMPARATOR" ERN TI' G CURRENT Q GENERATOR FILTER BAND PASS PAIENIEL EW 5.854.683

' W a v 1 l5 ALTERNATING COMPARATOR z E E' S BAND PASS FILTER drawing and appended claims.

In practicing our invention,'an alternating current I 1 DETECTOR TRACK CIRCUIT Our invention pertains to a detector'track circuit for railroads. More particularly, the invention pertains to a track circuit arrangement in which the change of frequency of the alternating current supply'voltage, when a train shunts the rails of a section, is detected to register the occupancy of the detector tracksection.

One necessary feature of any railroad signal, speed control, orautornatic train operation system is the continuous detection of trains in the various track sections involvedin order to avoid accidents due to loss of information as to location of the trains. Many types of track circuits for detectingthe'presence of trains are known and are in usein the railroad signaling and control arts. However, situations still occur in which anew and different track circuit arrangement is desirable in order to meet specific'situations. For. example, one such situation may occur where all of the wayside apparatus for the track circuit is to be located-at one end of the track section for any one of several reasons. Track circuits for such situations do exist but are not always suitable tance' is connected in series with the .transformersecondary winding and the rail loop.The] track section-is 7 formed by insulated joints at the near or apparatus'end and limited by'a crossbond connected between ,the'rails at the distant end. This fixes a non-shunted impedance condition for the secondary winding'circuit including the fixed inductance and the rail loop. The voltage drops resulting fromv the current flowing from the source throughthe fixed resistance and the, transformer primary, which of course reflects theinductive impedance of the secondary track circuit loop, are separately measured and applied to a voltage'comparator means. The measuring means may: be any applicable type i which will applyproper signals representing the two voltage drops to the comparator means. Thefixed resis-' tor and inductance haveselected values so that, when there is no train in the track section, thebasic frequency current flowing causes equal. voltage drops across the resistor and the transformer primary. However, a train shunting'the rails of the section changes therail impedance part of the secondary loop, which for-the track sectionconditions involved. Therefore a new type of trackv circuit for the detection of trains is needed for-unique situationswhich' may arise in railroad signalingand train control.

Accordingly, an object of our ivention is an improved detector track circuit for sections 'of railroad track.

"Another object of the invention is a track circuit which registers train occupancy by detecting the frequency change actuated in. the alternating track current .when the train shunts the rails of the track section.

Astill. further object of our invention is track circuitapparatus which detects the change in the circuit impedance when-a train shunts the rails 'of the section and varies the frequency of the input current to balance the impedance change and thus register the trackoccupied condition.

Still another object of the invention is a'track-circuit arrangement in which a change in the inductive impedance of the "shunted rails actuates a change in frequency of the alternating current source to balance the track or rail circuit impedance voltage drop with the voltage drop across a fixed resistor, with any shift in frequency away from a normal basic frequency actuating the registry of a track occupied indication.

change reflects through the transformer 'and varies the voltage drop across the transformer primary. The comparator means detects the unequal voltages. and outputs a shift signal which is coupled to the'source to vary its output frequency. The frequency is'changed until the measured voltage drops are again equal. Of course, i.f

the train is moving, aconstant change in the output fre- I quency is necessary as the shunt position moves throughout the section and the rail impedance continu ally varies. A second output from the alternating cur rent source is applied to a band pass filter tuned to pass only the basic frequency of the source. This'filter cont'rols a detector trackrelay which is energized only whenthe basic frequency is being generated. Therefore the track relay releases, similar to the conventional concept, when a shunt is'detected in the track section.

In other words, since the band pass filterpasses the Yet another-object of the invention is track circuit apparatus including means which compares thevoltage drops across a selected resistance and an inductive impedance including the rails and which varies the frequency of the sourceito equalize the voltage drop when a train shunt changes the rail impedance, such frequency change being registered as a track occupied indication.

Other objects,- features, and advantages of our invention will become apparent from the following specification when taken in connection with source is coupled across the rails of the detector track section through a transformer. This source is of the self generating type having normally a preselected basic frequency output but controllable with proper input signals to vary this frequency as required. A fixed resistance is connected in series with'the source and the primary of the coupling transformer while a fixed inducthe accompanying basic frequency only, when a shunt at any .position within the section actuates in a change in the output frequency, the train is detecte'd'and an occupiedindica- {tion registered by the relea'seof the track relay.

- I shall now describe ingreater detail a specif c setof apparatus embodying the concept of my invention and will then define the invention in the appendedclaims.

The, single drawing FIGURE is a diagrammatic illustration of one form of detector track circuit apparatus embodying our invention.- v

. Referring now to the drawing FIGURE, across the top are shown the two rails 7 and 80f a stretch of rail-- road trackfA track section T is set apart within this track circuit rail connections at the near end and crossbond 10. For purposes of this description, the presence of insulated joints will be assumed. Track circuit energy is supplied to the rails of section T from an alternating current generator source shown by a conventional block 3 since any one of several known types of alternating current generators may be used. This source of current 'or energy is coupled to the rails of section T at the near end through a coupling transformer 6, the generator output appearing on the leads 4 being connected across the primary winding of this transformer. The normal output of generator 3 has a preselected basic frequency which is maintained by a holding'signal, having predetermined characteristics, supplied over the input connection 16. However, this generator unit is also controllable by shift signals applied over lead 16 to vary the frequency of the output. This control input of the frequency is shown in a conventional manner since such controlled generators are knownin the art.-

' Connected in series with output leads 4 and the primary of transformer 6 is a resistor having a prese lected and fixed resistance value. Connected in series in the rail connections from the transformer'secondary is an inductor coil 12 which has a preselectedfixed inductance value. Obviously, the total impedance of the series connected loop including rails 7 and 8 of track section T to crossbond 10, the impedance of inductor 12,.and the impedance of the secondary winding is re flected through the coupling transformer into the primary winding. In other words, the impedance of the primary winding of transformer 6 reflects, in addition suring devices 13 and l4. Since voltage comparator circuits are known and anyone of several types may be used, a conventional block is used to illustrate this par- .ticular'element. Preferably the voltage measuring devices are a form of amplifier in order to isolate the voltage comparator from the conventional track circuit connections. The signals suppliedfrom units 13 and 14 represent the voltage drops across the transformer-6 primary winding and across resistor 5, respectively.

The voltage drop measured by device 13, of course, rel

fects the impedance existing in the secondary winding loop including rails 7 and 8 and inductor-l2. When the track section is clear, that is, unoccupied by any trian,

the signals supplied by units 13 and 14, that is, the measured voltagedrops, are equal as established by the selected values of resistor 5 and inductor 12. When this equality is detected by comparator 15,- the holding signal of predetermined characteristics is applied over lead 16 to the source to maintain the basic frequency output, This signal also provides a safety check of the continuity of lead 16 since generator 3 is so designed that the absence of any input signal will interrupt all output. When the applied voltage signals represent unequal voltage drops, comparator 15 responds to generate a variable control signal over lead 16 to generator 3 to vary the output frequency of this latter unit in order to change the voltage drop appearing across the transformer primary. This action is possible since resistor 5 is substantially a pure resistance while the impedance reflected into the primary winding is in a large measure of an inductive nature. The output frequency from generator3 is varied until the signals supplied by units 13 and 14 to the comparator are again equal. The

base of this equality, of course, is .the voltage drop across resistor 5 'which remains substantially the same under any output frequency condition:

A second output from generator 3 appearing on leads Q 17 is applied to a band pass filter'18. This filter unit is tuned to pass only signals having thebasic frequency of generator 3. Filter 18 must be an active type filter,- known in the art and thus shown by conventional block, in order to develop sufficient output energy'to energize the detector track relay TR. Relay TR is a conventional relay which, when energized, picks up'its contacts to close in their front position. Whenthe relay winding is deenergized, that is, receives no' or insufficient energy from the band pass filter, relay contacts .are released and close in their back position. For illustration, a single transfer set of front and back contacts of relay TR is shown which, in a well known manner, may be used to control a-signal, a traindetection indicator, or corresponding arrangements in a signaling system. Said in another way, when theoutput on leads 17 from generator '3, has the selected basic frequency, the signal or output is passed by band pass filter 18 in such a manner that sufficient energy is applied to relay TR to cause it topick up itscontacts. When the frequency appearing on output leads 17 is outside the basic frequency band, there is insufficient output from the band pass filter to energize relay TR which thus releases. Relay TR registers anunoccupied indication for section T when picked up and an occupied indication when released. I v

Summarizing briefly the operation of the trackcircuit apparatus shown in the drawing, it is illustrated in the condition which it assumes with no train occupyingor within section T between joints 11 and crossbond 10. The outputs from the alte'mating current generator 3 under this condition have the preselected basic frequency and the voltage drops across resistor 5 and the primary of transformer 6 are equal. Thus thevoltage signals produced by measuring devices 13 and 14 and applied to comparator 15 are also equal and the holding control signal is output from comparator 15 over lead 16 to generator. 3. The other output of the generator on leads 17, having the preselected basic frequency, is passed by filter l8 and sufficient energy is supplied to energize relay TR which thus closes its from contact,

as shown, to indicate the unoccupied conditionof track section T.

When a train enters section T, the impedance reflected through transformer 6 changes since the train shunt across the rails removes part of the impedance from the rail loop. Unequal voltage signals are therefore producedby devices 13 and l4 and applied to comparator 15. Under these conditions, the comparator produces a different control signal on-lead 16 which causes -a shift in the output frequency of generator 3. This shift continues until the signals from units 13 and 14 are again equal, that is, until equal voltage drops exist across resistor 5 and transformer 6. As previously mentioned, as long as the train moves through the section, this shifting action may be of a continuous nature in order to compensate for the" continuing change in rail impedance. Since, under these conditions, the output on leads 17 does not have the basic frequency, it is blocked by filter 18 and insufficient energy is produced to hold relay TR picked up. insufficiently energized,

relay TR releases and closes itsback contacts to thus 5. register an occupied condition for sectio'nT. It may be noted that, if a frequency meter is also connected across leads 17, the actual frequency may be used, by

properly calibrating the-frequency meter, to measure the distance to the existing rail shunt iri section T from the connection of the'track leads. Thus, in addition to an occupied indication resulting from'the release of relay TR, the properly calibrated frequency meter would give an indication to an operator of the distance from'the' rail connections, that is, basically the joints 11, to the nearest rail 'shunt or the distance to the train a or car.

The arrangement of our invention thus provides, in

a unique manner, a detector track circuit in which all apparatus is located at one end of the track section.'Al though additional apparatus is needed over that required for asim'ple,'direct current track circuit, an'ef- I I fective circuit for: detecting trains is nevertheless provided. The single location of all apparatus allows more economical installation and maintenance. Thetotal result is an effective, efficient, and safe detector-track circuit arrangement of the single ended type.

Although we have herein shown and described but a single form of track circuit apparatus embodying theconcept of our invention, it is to be understood that various changes and modifications. "may be made I therein within the'scope of the appended claims without departing fromthe spirit and scope of the invention.

Having now described the invention what we claim as new and desire to secure by Letters Patent, is:

I. Track circuit apparatus for detecting trains occu pying a section of railroad track, each rail of which forms a continuous electrical path fromthe near end to a distant end, comprising in combination,

a. a crossbond' connected between said rails at said distant end,

.b. a controllable frequency alternating current source having a basic frequency normal output,

- c. a first impedance'means connected to said rails at said near end to form a circuit path through said crossbond having a preselected inductive impedance at said basic frequency,

l said first impedance means further connected for coupling said source "to the circuit path including said rails,

d. asecond impedance means connected in series with said source in said circuit path and havinga constant value of impedance, at any frequency, se-

, lected to provide equal voltages across said first" andsecond impedance at said basic frequency, e, comparator means coupled for comparing the voltages developed across said-first and second imped ance means under all track occupancy conditions,

1. said comparator connected to said source for varying the output frequency from said basic frequency to equalize the-voltages across said first and second impedances whena rail shunt within said section changes said first impedance, and f. detection means coupled-to said source to receive an output having theexisting frequency, and responsive theretofor registering the unoccupied condition of said section only' when the received output has said basic frequency,

' 6. 2 I 1. saiddetection means registering an occupied condition of said section when said "output has any other frequency; l} 2. Trackcircuit apparatus'as defined in claim 1 in which? a. said first impedance means comprises,

, 1. a coupling transformer connected for coupling said source to said rails, ,7 2. a fixed valueof inductance connected in series with the transformer secondary winding and the rails and 3. the impedance of the rail loop'including said crossbond, g b. said second impedance means is a fixed value of resistance connected in'series with'said source and the transformer primary winding; 3. Track circuit apparatus-as defined in claim 2 in which said detection means comprises,

a. a band-pass filter device tuned to pass .only said b. a first measuring means connected forregistering thevoltage-developed across the transformer primary winding :in accordance with the impedance reflected fromsaid fixed circuit path, r I c. a second measureing means connected for registering. the voltage developed across said fixed resistance, d.'said first and second measuring means coupled for applying the registered voltage as first and second input signals, respectively, to said voltage compara- 101', I e. said voltage comparator alsocoupled to said I source for varying the source output frequency, when a train shunt varies the rail loopimpedance, until the input voltage signals are again equal 5. Track circuit apparatus'as defined in claim 4 in crossbond,

6. A detector track circuit arrangement for a section of railroad track, each rail of the section forming a con tinuous' electrical pathlfrom a near to'adistant end and crossbonded to the other rail at said distant end to form a rail loop with a predetermined impedance, compris ing in combination,

a. a source of alternating current having a preselected basic frequency, said sourcecontrollable for varying the output frequency in accordance with I selected input control signals, b. .a transformer connected for coupling said source to said rail loop, f v c. a first impedance connected in series with said rail loop for reflecting a variable inductive impedance, in accordance with the occupancy condition of said inductance and rail loop 50 'which' said track section limits are further established at said near end by insulated rail joints positioned for blocking the flow of rail current except toward said section, into the transformer primary winding connected to said source, V

d. a second impedance of preselected value fixed at all frequencies connected in series with said source and the transformer primary winding,

e. a comparator means coupled to said second impedance and said primary winding for comparing the voltages developed across these impedances in accordance with the track current required by the existingoccupancy condition of said section,

1. said comparator means also coupled for controlling said source to vary the output frequency to equalize the voltages developed across said sec ond impedance and theprimary winding, and

f. a detection means coupled for receiving an input signal from said source and responsive only to an input signal having said basic frequency for registeringan unoccupied section indication,

1. said detection means further responsive to the absence of said basic frequency input for registering a section. occupied indication.

7. A track circuitarrangement as defined in claim 6 existing frequency of the rail current supplied'by v said source and comprises,

l. the impedance of the rail loop established by saidcrossbond or by an intervening train shunt,

2. the impedance developed by a preselected fixed inductance connected in series with said .rail

loop, and

3. the impedance of the transformer secondary winding, and b. said second impedance is a preselected resistor having a resistive impedance substantially fixed at all frequencies.

8; A track circuit arrangement as defined in claim 6 in which said-detection means comprises,

a. anactive band pass filter tuned to pass only said basic frequency signals and connected, for receiving an input from said source having the existing frequency to which the source output has been controlled, and

p b. a detector track'relayenergized by said filter for indicating an unoccupied track section only when- 8 c. a voltage comparator connected for receiving as inputs the Ioutputsignals fromeach. measuring means and responsive thereto for producingxa se-' lected output control signal when said inputs repre sent unequal voltages, d. said voltage comparator coupled to said source for supplying said control signals to' vary the output frequency until the comparator input signals change to represent equal voltages.

10. A track circuit arrangement as defined in claim 6 in which,

a. said impedance reflected into said transformer primary winding is variable in accordance with, l. the existing frequency of the rail current supplied by said source,

2. the impedance of the rail loop established by lected resistive impedance substantially fixed at all.

frequencies, c. said comparator means comprises,

l. a first voltage measuring device coupled for producing an output signal representing the voltage I developed across said transformer primary winding due to the reflected impedances under eachv section occupancy condition, 1 2. a second voltage measuring'device coupled for producing an output signal representing the voltage developed across said resistor under each section occupancy condition, and

3. a voltage comparator connected for receiving the output'signals from each voltage measuring device and responsivethereto for producing 'a first output signalwhen the received signals represent equal voltages and a selected other outputsignal when the received signals represent unequal voltages,

4. said voltage comparator coupled'for supplying its output signals as control signals to said source, said first signal holding the source output at said basic frequency, each other signal varying the output frequency until the outputs of the voltage measuring devices again represent equal voltages, and a ,d. said detection means comprises,

1. an active band pass filter tuned to pass only said basic frequency and connected for receiving an input from said source having the existing fretrolled, and

2. a detector track relay energized by said filter for cate the track section occupied. 

1. Track circuit apparatus for detecting trains occupying a section of railroad track, each rail of which forms a continuous electrical path from the near end to a distant end, comprising in combination, a. a crossbond connected between said rails at said distant end, b. a controllable frequency alternating current source having a basic frequency normal output, c. a first impedance means connected to said rails at said near end to form a circuit path through said crossbond having a preselected inductive impedance at said basic frequency,
 1. said first impedance means further connected for coupling said source to the circuit path including said rails, d. a second impedance means connected in series with said source in said circuit path and having a constant value of impedance, at any frequency, selected to provide equal voltages across said first and second impedance at said basic frequency, e. comparator means coupled for comparing the voltages developed across said first and second impedance means under all track occupancy conditions,
 1. said comparator connected to said source for varying the output frequency from said basic frequency to equalize the voltages across said first and second impedances when a rail shunt within said section changes said first impedance, and f. detection means coupled to said source to receive an output having the existing frequency, and responsive thereto for registering the unoccupied condition of said section only when the received output has said basic frequency,
 1. said detection means registering an occupied condition of said section when said output has any other frequency.
 2. a detector track relay energized by said filter for indicating the track section unoccupied only when the filter input is at said basic frequency, said relay otherwise being deenergized to indicate the track section occupied.
 2. a fixed value of inductance connected in series with the transformer secondary winding and the rails and
 2. Track circuit apparatus as defined in claim 1 in which, a. said first impedance means comprises,
 2. a second voltage measuring device coupled for producing an output signal representing the voltage developed across said resistor under each section occupancy condition, and
 2. the impedance of the rail loop established by said crossbond or by an intervening train shunt across said rails,
 2. the impedance developed by a preselected fixed inductance connected in series with said rail loop, and
 3. the impedance of the transformer secondary winding, and b. said second impedance is a preselected resistor having a resistive impedance substantially fixed at all frequencies.
 3. Track circuit apparatus as defined in claim 2 in which said detection means comprises, a. a band pass filter device tuned to pass only said basic frequency and connected to receive an output from said source, b. a detector track relay controlled by said filter device to a first and a second position for regiStering unoccupied and occupied conditions of said section, respectively, as the received output has said basic frequency or another frequency.
 3. the impedance of the rail loop including said crossbond, b. said second impedance means is a fixed value of resistance connected in series with said source and the transformer primary winding.
 3. the impedance of a preselected fixed inductance connected in series with said rail loop, and
 3. a voltage comparator connected for receiving the output signals from each voltage measuring device and responsive thereto for producing a first output signal when the received signals represent equal voltages and a selected other output signal when the received signals represent unequal voltages,
 4. said voltage comparator coupled for supplying its output signals as control signals to said source, said first signal holding the source output at said basic frequency, each other signal varying the output frequency until the outputs of the voltage measuring devices again represent equal voltages, and d. said detection means comprises,
 4. the impedance of the transformer secondary winding, b. said second impedance is a resistor having a preselected resistive impedance substantially fixed at all frequencies, c. said comparator means comprises,
 4. Track circuit apparatus as defined in claim 3 in which said comparator means comprises, a. a voltage comparator operable for comparing the relative voltages of first and second input signals, b. a first measuring means connected for registering the voltage developed across the transformer primary winding in accordance with the impedance reflected from said fixed inductance and rail loop circuit path, c. a second measureing means connected for registering the voltage developed across said fixed resistance, d. said first and second measuring means coupled for applying the registered voltage as first and second input signals, respectively, to said voltage comparator, e. said voltage comparator also coupled to said source for varying the source output frequency, when a train shunt varies the rail loop impedance, until the input voltage signals are again equal
 5. Track circuit apparatus as defined in claim 4 in which said track section limits are further established at said near end by insulated rail joints positioned for blocking the flow of rail current except toward said crossbond,
 6. A detector track circuit arrangement for a section of railroad track, each rail of the section forming a continuous electrical path from a near to a distant end and crossbonded to the other rail at said distant end to form a rail loop with a predetermined impedance, comprising in combination, a. a source of alternating current having a preselected basic frequency, said source controllable for varying the output frequency in accordance with selected input control signals, b. a transformer connected for coupling said source to said rail loop, c. a first impedance connected in series with said rail loop for reflecting a variable inductive impedance, in accordance with the occupancy condition of said section, into the transformer primary winding connected to said source, d. a second impedance of preselected value fixed at all frequencies connected in series with said source and the transformer primary winding, e. a comparator means coupled to said second impedance and said primary winding for comparing the voltages developed across these impedances in accordance with the track current required by the existing occupancy condition of said section,
 7. A track circuit arrangement as defined in claim 6 in which, a. said variable impedance reflected into said transformer primary winding is in accordance with the existing frequency of the rail current supplied by said source and comprises,
 8. A track circuit arrangement as defined in claim 6 in which said detection means comprises, a. an active band pass filter tuned to pass only said basic frequency signals and connected for receiving an input from said source having the existing frequency to which the source output has been controlled, and b. a detector track relay energized by said filtEr for indicating an unoccupied track section only when the filter input is at said basic frequency, said relay otherwise deenergized to indicate an occupied track section.
 9. A track circuit arrangement as defined in claim 6 in which said comparator means comprises, a. a first measuring means coupled to said transformer primary winding for producing an output signal representing the voltage developed across said reflected impedance under each section occupancy condition, b. a second measuring means coupled for producing an output signal representing the voltage developed across said second impedance under each section occupancy condition, c. a voltage comparator connected for receiving as inputs the output signals from each measuring means and responsive thereto for producing a selected output control signal when said inputs represent unequal voltages, d. said voltage comparator coupled to said source for supplying said control signals to vary the output frequency until the comparator input signals change to represent equal voltages.
 10. A track circuit arrangement as defined in claim 6 in which, a. said impedance reflected into said transformer primary winding is variable in accordance with, 